The present invention relates to a solid state imaging device in which enlargement of dynamic range is made easy.
As for a solid state imaging device which is one of electronic devices, a CCD solid state imaging device (so-called CCD image sensor) which is a charge transfer type and a CMOS solid state imaging device (so-called CMOS image sensor) which reads out by addressing X-Y addresses are representative. Any one of these solid state imaging devices is similar in that incident light which enters into a photodiode arranged two-dimensionally is converted photo-electrically and one charge (for example, electron) thereof is made to be a signal charge.
In a camera using one of these solid state imaging devices of a CCD type or a CMOS type, amount of light is set to a standard setting level usually by using an aperture diaphragm of a lens or the like. For example, it can be said in a case when a landscape and clouds floating on the sky are to be taken a picture together or also, for example, in case of taking a picture indoors and in a case when an indoor ornament and a landscape on the outside of window are desired to be taken a picture together, but pictures actually taken by a camera would become very flat pictures without depth, because these solid state imaging devices possess saturation characteristic with respect to a strong light. Also, a request for high definition (for example, 2 million pixels) is strong for a recent solid state imaging device and miniaturization of the cell size thereof is being attained (for example, 3 micron angle), and an amount of maximum handling charge (Qs) is becoming smaller such that the number of electrons is becoming 6,000 to 10,000. Further, it has become a situation in which the setting level cannot be avoided from being raised in order to suppress an influence of a light shot noise in a standard setting state and an influence of a fixed pattern noise or a dark current and taken pictures are becoming pictures without depth all the more.
As means for solving these problems, a CCD solid state imaging device of a frame transfer system (see below patent reference 1) controls the amount of accumulated charge and recombines the overflow charge with the peripheral channel stop (in this case, without providing n-region), but actually a blooming phenomenon occurs in this frame transfer type.
In a CCD solid state imaging device of an inter transfer system (see below Patent Reference 2), a lateral overflow drain structure is employed and by controlling its overflow control electrode and further, in a CMOS solid state imaging device (see below non-patent reference 1), by controlling a reset voltage, Qs of each solid state imaging device is changed during the light acceptance and the relation between the amount of light and the output is made to possess γ characteristic for a conventional linear relation so as to pseudo-increase Qs.
On the other hand, in order to promote miniaturization pixel cell size, there is known a CCD solid state imaging device of a vertical overflow structure which executes sweeping out of a signal charge to the substrate side. In the CCD solid state imaging device of the vertical overflow structure, a constant substrate voltage is applied to the substrate during the light acceptance and it is constituted when an electronic shutter is carried out such that the substrate potential is changed so as to sweep out a signal charge to the substrate side (see below patent reference 3).
Also, γ correction is carried out by bending the linear curve of a TV signal process, but γ correction has not been employed in the vertical overflow structure.
[Patent Reference 1] U.S. Pat. No. 3,953,733 (RCA; 1975)
[Patent Reference 2] Jap. laid-open patent publication S54-51318
[Patent Reference 3] Jap. laid-open patent publication H2-40956
[Non-patent Reference 1] IEEE JSSC Vol.33, PP2081 (MIT; December, 1998)
And now, also in the above mentioned solid state imaging device of the vertical overflow structure, enlargement of the dynamic range is attempted by applying γ characteristic to the relation between the amount of light and the amount of output charge, that is, enlargement of the dynamic range is attempted, because it is desired to pretend such that the amount of accumulated charge around 3 micron angle at the present situation can be seen to be large even if it is a pseudo-operation.